Method of treating electronic-emission devices



Patented Mar. 6, 1928. I

UNITED STATES PATENT OFFICE.

MAURICE ID. SABBEY,

YORK.

METHOD O1 TREATING ELECTRONIC-EMISSION DEVICES.

No Drawing.

This invention relates to devices of the type utilizing electronic emission from heated cathodes, of which class of devices the audion tube is an example; and comprises a novel 5 method for improving the emissive characteristics of such devices. In its preferred embodiment my method improves the emissivity' of the heated cathode element of such tubes in two important respects; first, by increasing the em'ssivity under normal or even abnormal operating conditions; and second, by rendering the emissive element or cathode less sensitive to conditions destructive 'of or injurious to its emissivity. I will describe my invention with specific reference to thetreatment of a tubes of types commonly used ception, but it is to be understood that these examples are illustrative only, and that the method is applicable with appropriate modification of its conditions to a wide variety of devices depending upon electronic emissivity from heated cathodes.

The filaments of such tubes are commonly made of tungsten, which is either admixed with a relatively small roportion of tho1'i um oxid (thoria) or a oyed with metallic thorium. Either of these additions improves the emissivity of the filament, although the characteristics offthe two types of filament are uite different in certain respects. My met d, now-to be described, is a plicable to both the alloy and oxid types 0 filament, tending in either case to increase the emissivity, and markedly improving the stability of the filament, thatis,

reducing its sensitlveness to otherwise destructive conditions.

It is well known that the emissivity of tho'riated filaments is rapidly reduced when they are subjected at an a normally hi h temperature (that is to say, at a filament vo tage substantially above the normal operating voltage) to a high plate voltage: and my experiments have demonstrated that thorium alloy filaments act under these conditions in Accordingly the following through a milliammeter to Application filed October 21, 1925. Serial No. 64,056.

a somewhat similar manner although to a lesser extent. It is a characteristic feature of my invention that it utilizes as the first or preliminary step in the improvement of the filament, this supposedly destructive action of high plate voltage at high temperature, preferably continuing this action until the emissivity has fallen to half or less of its initial value. Thereafter, as a'second operating step,- the plate voltage is discontinued and the high filament voltage continued for a further period, and until the emissivity of the filament is restored to the desired degree, which is usually but not necessarily higher than the initial emissivity.

v It will readily be understood that the numerical. value of the filament and plate (or grid) voltages, as well as the-duration of the treatments, may vary somewhat widely according to the size and type of the audion tube or other electron emissive device. examples are to be regarded .as illustrative only. In these examples the tube designated thoriated filament was of the type commercially known as U. V. 201 A, having in addition to plate and grid, a filament of tungsten containing a small admixture .of thoria, and designed for operation at 5 volts and 0.25 amperes. The tube designated"alloy fila ment was similar in size and construction, but contained a tungsten filament having alloyed therewith approximately one of metallic thorium. In both cases, tive terminal of a 100 volt battery was connected to a filament terminal, the positive terminal of the same battery being connected both plate and grid. Under these conditions the milliamme- 85 ter indicated the total-emission, and it was possible to note the decrease in emission under the stripping action of the ionic the nega- I the test was continued until the emission fell to or below 14 milliamperes.

Thoriated filament.

Emission Mutual conductance (milliamperes) (miero-mhos) Elapsed time w No.1 No 2 No.3 No.1 l No.2 No.3

Start 860 1 minute 780 3 660 5 560 10 420 420- Alloy filament;

Thereafter jected to a stripping and aging treatment according to my invention, and as below dethese several tubes were subscribed: and upon re-testing under precisely the same conditions as before, it was found thattheir initial emissivity had been restored or even increased, and that they were dis-. tinctly less sensitive to the bombardment. The tubes, after treatment, gave results as follows:

Thoriated filament.

- Emission Mutual conductance (milliamperes) (mlcro-mhos) Elapsed time a No 1 No. 2 N0. 3 No. 1 No. 2 No. 3

Alloy filament.

Emission Mutual conduct- (milliamperes) ance (mlcro-mhos) Elapsed time No.4 No.5 No.4 No.5

By comparing the behavior of these tubes before and after treatment it will be observed that the rate of drop of emission is in all cases much less after treatment: in other words the filaments have been rendered far less sensitive to the ionic bombardment to which they are subjected either in norof which was connected to both plate and grid, whereby the filament a very intensive stripping ing this stripping step the plate voltage was discontinued and the superheating of the filament under the 6.7 volt filament current was continued for one hour.

As already'explained these specific values apply only toparticular types-of tubes, and it is to be understood that the. optimum treating. conditions may vary rather widely with differing types of tubes or even with tubes of the same type made by different manufacturers. But so far as my observawas subjected to action. Followtion has extended the optimum conditions in all cases involve superheating the cathode (filament) in presence of a h1gh anode poby a further or ageing or with so low a potential as fere with the ageing nitude to amount to a continuance of the fiist or stripping to continue the absence of anode mal filament voltages, that is to say under superheat conditions, I may with less advantage substitute a more prolonged ageing treatment at temperatures equal to or even somewhat below normal operating temperatures; but I regard such procedure as both less etfective and less desirable than the continuance of the snperheat conditions during his ageing step.

claim:

1. Method of treating electronic emission devices to improve their emissive characteristics, comprisin superheating the cathode in presence of a igh anode potential to reduce the emissivity, and thereafterfurther heating the cathode in absence of anode potential.

operation. While I prefer heating of the cathode 1n 2. Method of treating electronic emission devices to improve their emissive characterstics, comprising superheating the cathode in presence of a hig anode potential until the emissivity under normal operating conditions has fallen to less than one-half its potential under supernorin presence of a super-normal anode potential to reduce the emissivity, and thereafter further heatin the cathode in absence of anode potentia 4. Method of treating electronic emission devices to improve their emissive characteristics, comprising superheating the cathodein-presence of a super-normal anode potential until the emissivity under normal operating conditions has fallen to less than onehalf its initial value, and thereafter further heating the cathode in absence of anode potential.

5.'Method of treating electronic emission devices to improve their emissive characteristics, comprising superheating the cathode in presence of a high anode potential to r e duce the emissivity, and thereafter further superheating the cathode in absence of anode potential.

6. Method of treating electronic emission devices to improve their emissive characteristics, comprism superheating the cathode in presence of a igh anode potential until the emissivity under normal operating conditions has fallen to less than one-half its initial value, and thereafter further superheating' the cathode in absence of anode potential.

7. Method of treating electronic emission devices to improve their emissive characteristics, comprising superheating. the cathode in presence of a super-normal anode potential to reduce the emissivity, and thereafter further super-heating the cathode in absence of anode potential.

8 Method of treating electronic emission devices to improve their emissive characteristics, comprising superheating the cathode in resence of a super-normal anode potenti'a until the emissivity under normal operating conditions has fallen to less than onehalf its'initial value, and thereafter further superheating the cathode in absence of anode potential.

In testimony whereof, I afiix my si ature.

MAURICE D. SAR BY. 

